Light guide illumination devices

ABSTRACT

A light-guide illumination device and system comprises a light source, a light redirecting slab and a light guide slab assembly. The light redirecting slab includes a generally planar face having optical redirecting elements, the optical redirecting elements having respective optical coupling surfaces situated distally from the planar face. The light guide slab assembly includes a planar face having an optically transmissive interface layer assembled onto a first planar face of the light guide slab and optically coupled to receive transmitted light directed from the light source. The light guide slab is pressed onto the redirecting slab such that the interface layer is deformed, creating optical bonds at the optical coupling surfaces of the optical redirecting elements, the formed optical bonds providing optical apertures for light transmission therethrough.

FIELD

The present disclosure relates generally to an apparatus and systemhaving a direct optical coupling interface for light guided illuminationdevices.

BACKGROUND

In an effort to protect Earth's environment and to conserve naturalresources, the reduction of greenhouse gas emissions has been identifiedas a priority by governments around the world. One way to reducegreenhouse gas emissions is to reduce energy consumption. Theconsumption of energy can be reduced by using energy efficient devices,including illumination devices.

Optical illumination devices and systems using planar or slab lightguides are energy efficient illumination devices. Such illuminationdevices typically include various layers of optically transmissivelayers or media. Conventionally such illumination devices may be dividedinto a layer that receives and guides light from one or more lightsources (in the present application called a light guide layer—but alsocalled a variety of other names in the art) for insertion into a layerthat redirects the light (in the present application called a lightredirection layer—but also called by a variety of other names in theart) for emission from the illumination device. Depending on theconfiguration and construction of a particular illumination device,these layers may be areas of a unitarily manufactured structure or maybe separate physical structures that have been separately manufacturedand subsequently brought together to form a single structure thatoperates as a unit. Some examples of planar illumination devices areshown in U.S. Patent Application Publication No. US2010/0202142.

Where the layers are manufactured separately and are subsequentlyassembled to form a unit, the interfaces between the layers inherentlypresent discontinuities in the optical transmission path, such thatlight being transmitted can be subject to reflection losses, morecommonly known as Fresnel losses in the art, particularly when thelayers are misaligned. The degree of Fresnel losses affecting theefficiency of light transmission depends on the quality of the opticalbond or coupling existing at a given optical transmission interface andthe quality of the fabrication of the optical components.

Current conventional planar illumination devices that are highlyefficient are therefore not easy to manufacture as extreme precision,both in the fabrication of the layers and in their alignment when theyare brought together to form a unit, is required. Small defects eitherin fabrication or in alignment will have a very significant negativeeffect on the percentage of light received from the light source thatthe illumination device is able to emit, and must generally be avoided.

To the extent that optical coupling across the different lighttransmission materials and layers used in light guide illuminationdevices can be made more efficient, such as (but not limited to)reducing Fresnel losses, a higher performance product having loweredenergy consumption while providing a higher-intensity output, can beachieved.

SUMMARY OF THE INVENTION

Provided is an illumination device comprising at least one light source,a light redirecting slab made of optically transmissive material andcomprising an optical output surface and an array of optical redirectingelements, each of the optical redirecting elements having an opticalcoupling surface situated distally from the optical output surface andat least one light redirecting surface for receiving light from theoptical coupling surface and redirecting the light received therefromtoward the optical output surface for emission therefrom; asubstantially planar light guide slab made of an optically transmissivematerial and having a first surface, a second surface opposite the firstsurface and at least one input surface, the at least one input surfacefor receiving light from the at least one light source; and an array ofoptical apertures optically coupling the first surface of the lightguide slab and the optical coupling surfaces of the light redirectingslab, the optical apertures formed by at least one deformed opticalcoupling element. The first surface, the second surface and the at leastone deformed optical coupling element structured and arranged one withrespect to the other such that light entering the light guide layer isguided through the light guide layer via one or more reflections forinsertion into the light redirecting slab.

In one embodiment, the device further comprises at least one secondaryoptical element redirecting at least a portion of the light from one ormore of the at least one light source into the light guide slab, eachsecondary optical element in optical communication with one or more ofthe at least one input surface of the light guide slab and with one ormore of the at least one light source. In a further embodiment, theillumination device further comprises at least one deformable secondaryoptical coupling element, each secondary optical coupling elementcoupling one of the at least one optical input surface of the lightguide layer to an optical exit surface of one of the at least onesecondary optical element. The secondary optical element is situatedabove the light guide slab and one of the at least one light source inyet another variation.

In yet another embodiment, the deformed optical coupling element is asingle optically transmissive interface layer disposed between the lightguide slab and the light redirecting slab to form the array of opticalapertures. In an alternate arrangement, the deformed optical couplingelement is a plurality of optically transmissive interface layers, eachone of the plurality of optically transmissive interface layers disposedbetween the light guide slab and the optical coupling surface of one ofthe array of optical redirecting elements to form one of the array ofoptical apertures. In another variation, the deformed optical couplingelement is at least a portion of each of the optical redirectingelements including the optical coupling surface of the opticalredirecting elements.

The deformed optical coupling element may comprise a soft polymermaterial that is elastomeric, for example, a silicone material.

In an embodiment, the optical output surface may comprise collimatingelements. In another variation, the optical output surface may besubstantially planar.

The light redirecting surface, in one embodiment, redirects light viatotal internal reflection. In a further arrangement, the lightredirecting surface may include a parabolic section in cross-section.

In one embodiment of the illumination device, each of the opticalredirecting elements comprises a first light redirecting surface forreceiving light that generally travelled in a first direction throughthe light guide slab and a second light redirecting surface forreceiving light that generally travelled in a second direction, oppositethe first direction, through the light guide slab, both of the first andthe second light redirecting surfaces being optically coupled to theoptical coupling surface of the said optical redirecting element andbeing structured and arranged to redirect light impinging thereon towardthe optical output surface, wherein at least one peripheral edge of thelight guide slab comprises a reflective element to reflect light thatwould otherwise escape from the light guide slab back into the lightguide slab. In a further arrangement, the reflective element is a mirrorcoating. In yet another variation, the reflective element is a prism forredirecting light via total internal reflection back into the lightguide slab.

In another embodiment of the illumination device, the first surface andthe second surface of the light guide slab are substantially planar andparallel to one another. In a further variation, the light guide slab isgenerally wedge-shaped and tapers away from the at least one lightsource. In yet another variation, the first surface of light guide slabis stepped.

In yet another arrangement of the illumination device, the first surfaceof the light guide slab comprises a planar light guide layer and aplurality of light steepening elements extending from the planar lightguide layer, each of the light steepening elements comprising at leastone reflective surface for moderating the steepness of angles of thelight being transmitted through the light guide slab to provide outputlight of generally uniform intensity across the light output surface,the steepness of the reflective surface increasing progressively fromthe at least one light source toward a peripheral edge of the lightguide slab.

The illumination device, in yet another variation, may have a lineargeometry, wherein the optical redirecting elements are arranged inparallel lines. The light source may be located along a peripheral edgeparallel to the optical redirecting elements, in a further arrangement.IN yet another arrangement, the illumination device may have a centralaxis, wherein the at least one light source is located along the centralaxis and wherein each of the optical redirecting elements are annular,of a sequentially increasing diameter and concentrically arranged aboutthe central axis.

In yet another embodiment of the illumination device, the opticalredirecting elements are annular and are located along substantiallyconcentric circle arcs and the input surface is shaped as a circle arcsubstantially concentric with the optical redirecting elements and formsa portion of the peripheral edge of the light guide slab.

In yet a further variation of the illumination device, the lightredirecting slab has a circular circumference, and the concentric circlearcs along which the optical redirecting elements are located areeccentric with the circular circumference of the light redirecting slab.The optically transmissive material of both the light redirecting slaband the light guide slab may be elastomeric.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described by way of example only, with referenceto the following drawings in which:

FIG. 1A shows an illumination device including one embodiment of anoptical coupling interface directing transmission of light from a lightsource;

FIG. 1B shows further detail of the optical coupling interface of theillumination device of FIG. 1A;

FIG. 2 shows the illumination device including an optical apertureinterface in an alternate embodiment;

FIG. 3A shows an embodiment of the illumination device includingbi-directional redirecting elements arranged for collimated lightoutput;

FIG. 3B shows further detail of the illumination device of FIG. 3A;

FIG. 4A shows an embodiment of the illumination device having anarrangement of varying light redirecting angles for collimated lightoutput;

FIG. 4B shows further detail of the illumination device of FIG. 4A;

FIG. 5 shows an embodiment of the illumination device including clampingmeans;

FIG. 6 shows an alternate embodiment of the illumination device having astepped light guide and redirecting elements of varying size;

FIG. 7 shows an alternate embodiment of the illumination device having awedge shaped light guide;

FIGS. 8A, 8B and 8C show an illumination device made of a flexible lighttransmissive material;

FIG. 9A shows another embodiment of the illumination device havingbi-directional redirecting elements arranged for collimated lightoutput; and

FIG. 9B shows a revolved embodiment of the illumination device.

FIG. 10 shows a linear embodiment of the illumination device having alight cylinder at one planar edge surface.

FIG. 11A shows a top perspective view of a semi-broad beam embodiment ofthe illumination device of the present invention;

FIG. 11B shows a cross section of the semi-broad beam embodiment of theillumination device of FIG. 11A;

FIG. 12A shows a top perspective view of another embodiment of theillumination device of the present invention having revolved lightredirecting elements and linear light collimating lenses;

FIG. 12B shows a cross section of the illumination device of FIG. 12A;

FIG. 13A shows a perspective view of an embodiment of the illuminationdevice of the present invention where the light source is edge-mounted,having concentric partially revolved light redirecting elements andlinear light collimating lenses

FIG. 13B shows a cross section of the illumination device of FIG. 13A;

DETAILED DESCRIPTION

FIGS. 1A and 1B show an illumination device 100 having optical couplingelement providing optical apertures for transmission of light from alight source therethrough to a light output surface 120.

The illumination device 100 includes a light source 101, and optionally,a secondary optical element 102 (a supplementary light dispersal opticfeature) directing the transmission of light from the light source 101into a light guide slab 108. The illumination device 100 furthercomprises an optically transmissive interface layer 107 that is anoptical coupling element between the light guide slab 108 and a lightredirecting slab 103. The light redirecting slab 103 includes agenerally planar portion 104 having an output surface 120 and aplurality of optical redirecting elements 105, the optical redirectingelements 105 each having an optical coupling surface 106 situateddistally from the output surface 120.

The light redirecting slab may be made of any suitable opticallytransmissive material, such as glass or injection molded poly(methylmethacrylate) (PMMA). Other non-limiting examples of light transmissivematerials include Cyclo Olefin Polymers (COP), Cyclo Olefin Copolymers(COC), other polymeric materials, and combinations thereof.

The light guide slab 108 may similarly be made of any suitable opticallytransmissive material, such as glass or PMMA, and has an input surface122 for accepting light from the light source 101, a generally planarfirst surface 123 and a generally planar second reflective surface 124.The optically transmissive interface layer 107 may be comprised of asoft material such as a silicone which is deformable under an appliedpressure, and is overmolded, or bonded with an optically transmissiveadhesive to the planar first surface 123 of the light guide slab 108.Alternatively, but less desirably, the optically transmissive interfacelayer 107 may be formed separately from the light guide slab 108 andassembled onto the planar first surface 123. In the latter embodiment,the optically transmissive interface layer 107 is optically coupled orbonded to the light guide slab 108 wherever sufficient pressure isapplied to deform the optically transmissive interface layer 107 againstthe light guide slab 108, thereby eliminating air between the opticalcoupling surfaces 106 and the interface layer 107. Suitable silicone(deformable) will be in the range of 20-60 on the Shore OO scale or 1-14on the Shore O scale, and injection molded Evonik™ 8N will be in therange of 1-35 on the Brinell scale or 75-100 on the Rockwell M scale.The light guide slab 108 and the optically transmissive interface layer107 are collectively referred to as a light guide assembly 126.

The light guide slab 108 is optically coupled to and receivestransmitted light directed from the secondary optical element 102through the input surface 122. Optical bonds creating optical apertures109 for coupling light from the light guide slab 108 to the lightcoupling surfaces 106 of the light redirecting slab 103 are formed ateach optical coupling surface 106 of the optical redirecting elements105 when the light redirecting slab 103 is pressed onto the opticallytransmissive interface layer 107 redirect, redirecting. The light guideslab 108 is otherwise separated from the light redirecting slab 103 byareas 125.

The light redirecting slab 103 may further include an arrangement ofcollimating elements such as collimating lenses 110 to providecollimated light output 111 at the light output surface 120. Where theentire optically transmissive interface layer 107 is optically bonded tothe light guide slab 108, light is guided by and travels within thelight guide assembly via reflections on the first surface 150 of theoptically transmissive interface layer 107 and the planar secondreflecting surface 124. Where areas 125 are comprised of a material orgas having an index of refraction that is lower than the material of thelight guide slab 108, the reflections may be total internal reflections.The range of angles at which light enters the waveguide may be definedby the geometry of the secondary optic 102.

The light source 101, may be, but is not limited to one or more LEDs, acompact fluorescent tube, a small incandescent light bulb or solar lighttransmitted via optical fibres, and may be located along an axis ofsymmetry 121 of the illumination device 100. The illumination device 100may have a linear geometry or a revolved geometry. An illuminationdevice 100 with a linear geometry has redirecting elements 105 that arearranged along substantially parallel lines. An illumination device 100with a revolved geometry is radially symmetric about the axis ofsymmetry 121, with redirecting elements 105 forming concentric ringsabout the axis of symmetry 121.

FIG. 1B shows further configuration detail of the optical apertures 109,formed by applying pressure on or squeezing the optically transmissiveinterface layer 107 between the optical coupling surfaces 106 and thelight guide slab 108 of the illumination device 100 depicted in FIG. 1Asuch that an optical bond is formed therebetween. Light 112 emitted fromthe light source 101 is guided by the light guide slab 108 until itescapes through the optical apertures 109 into the light redirectingslab 103.

Each optical redirection element 105 is associated with an opticalaperture 109 and comprises a light redirecting surface 115. Each lightredirecting surface 115 receives at least a portion of the light 112passing through the corresponding optical aperture 109 and redirects thereceived light at an angle of redirection 114 into the planar portion104. Each light redirecting surface 115 can be a reflective surface. Byway of example, the reflective surface can reflect light by totalinternal reflection or off of a reflective coating (sometimes referredto in the art as mirror coating). In the event that light is reflectedvia total internal reflection, this is caused by the difference inrefractive indices of the light redirecting slab 103 and the materialfilling the areas 125 between the light guide assembly 126 and the lightredirecting slab 103, which in this case may be air. In the event thatthe light redirecting surfaces are mirror coated, not-limiting examplesof reflective materials include metals such as aluminum or silver, or adielectric.

Each of the optical redirecting surfaces 115 of the redirecting elements105 can be a parabolic section in cross-section. Where the parabolicsection has a focal point in the vicinity of the optical aperture 109,the light entering the light redirecting slab 103 through thecorresponding optical aperture 109 will be redirected by the redirectingsurface 115 toward the optical output surface 120 as substantiallyparallel rays. The geometry of the optical redirecting elements 105 maybe configured to provide effectively varying angles of redirection 114,for example, by steepening the light redirecting surfaces 115 of theoptical redirecting element 105. The light redirecting surfaces 115 andcollimating lenses 110 may be arranged such that light 111 exiting theillumination device 100, through the light output surface 120, iscollimated.

FIG. 2 shows another embodiment of an illumination device 200. Theillumination device 200 includes a light source 201, a secondary opticalelement 202 directing transmission of light from the light source 201, alight redirecting slab 218 and a light guide slab 208. The lightredirecting slab 218 comprises an optically transmissive layer 203having a planar face 204 and an output surface 220, and an array ofoptical redirecting elements 205. The optically transmissive layer 203may be made of any optically transmissive material such as glass orinjection molded PMMA. The array of optical redirecting elements 205 aremade of a deformable, optically transmissive material having a similarindex of refraction to that of the optically transmissive layer 203. Forexample, the optical redirecting elements 205 can be injection moldedsoft silicone which is deformable under pressure, and overmolded orbonded with an optically transmissive adhesive onto the planar face 204of the optically transmissive layer 203 to form the redirecting slab 218and also serve as optical coupling elements. The optical redirectingelements 205 include redirecting surfaces 215 and optical couplingsurfaces 206 situated distally from the planar face 204. The outputsurface 220 of the light redirecting slab 218 may further include anarrangement of collimating elements such as collimating lenses 210,which in conjunction with the redirecting surfaces 215 providecollimated output light 211 at the light output surface 220.

The illumination device 200 has an axis of symmetry 221 along which thelight source 201 lies. In a linear embodiment, the redirecting elements205 are arranged along substantially parallel lines about the axis ofsymmetry 221. Alternatively, the illumination device 200 may be radiallysymmetric about the axis of symmetry 221, the redirecting elements 205and lenses 210 forming concentric rings about the axis of symmetry 221.

The light guide slab 208 has a first reflecting surface 223 and a secondreflecting surface 224, both of which may be planar surfaces. The lightguide slab 208 is in optical communication with the secondary opticalelement 202 and may be optically coupled thereto by a secondary opticalcoupling element 227. The secondary optical coupling element 227 is madeof an optically transmissive material that is deformable under anapplied pressure, such as silicone. The light guide slab 208 may besecured against the redirecting slab 218 by one or more fasteners suchas clamps, to apply a constant and controlled pressure, therebydeforming the optical coupling surfaces 206 and creating opticalapertures 209 between the optical coupling surfaces 206 and the lightguide slab 208.

Light travels within the light guide slab 208 via reflections betweenthe first reflecting surface 223 and the second reflecting surface 224.The reflections may be total internal reflections where areas 225between the light guide slab 208 and the redirecting slab 218 are filledby a material or gas with an index of refraction that is lower than thatof the light guide slab 208 (e.g. where areas 225 are air gaps).

Each redirecting element 205 is associated with an optical aperture 209and each light redirecting surface 215 receives at least a portion ofthe light 212 that passes through the corresponding optical aperture 209formed at the coupling surface 206 and redirects the received light intothe optically transmissive layer 203.

FIG. 3A shows an embodiment of an illumination device 300, having alight source 301, a secondary optical element 302, a light redirectingslab 303, a bi-directional light guide slab 308, an opticallytransmissive interface layer 307 between the light redirecting slab 303and the bi-directional light guide slab 308, and a central axis ofsymmetry 321.

The light guide slab 308 comprises a planar first surface 323 and aplanar second reflective surface 324, and is optically coupled to thesecondary optical element 302, which directs the transmission of lightfrom the light source 301.

The redirecting slab 303 has redirecting elements 305 and a light outputsurface 320, and can be made of any optically transmissive material,such as glass or injection molded PMMA. In the illustrated embodiment,each redirecting element 305 comprises an optical coupling surface 306,and two parabolic redirecting surfaces 315 a and 315 b to collimatelight from the light guide slab 308, travelling in opposite directions.The illumination device 300 may have a linear geometry or a revolvedgeometry. An illumination device 300 with a linear geometry hasredirecting elements 305 that are arranged along substantially parallellines about the axis of symmetry. An illumination device 300 with arevolved geometry is radially symmetric about the axis of symmetry 321,with redirecting elements 305 forming concentric rings about the axis ofsymmetry 321.

The optically transmissive interface layer 307 which serves as anoptical coupling element is made of a soft material such as siliconewhich is deformable under an applied pressure, and may be overmolded orchemically bonded with an optically transmissive adhesive onto the firstplanar reflective face 323 of the light guide slab 308, or simply placedbetween the light guide slab 308 and the redirecting slab 303 during theassembly of the illumination device 300, as in illumination device 100.When pressed onto the optically transmissive interface layer 307, thecoupling surfaces 306 of the light redirecting slab 303 form an array ofoptical apertures 309 where the coupling surfaces 306 of the redirectingelements 305 make contact with and apply pressure to deform theoptically transmisssive interface layer 307. The optical apertures 309optically couple the light guide slab 308 to the light redirecting slab303.

Light 312 within the light guide assembly (comprising the light guideslab 308 and the optically transmissive interface layer 307) travels viareflections on the first surface 350 of the optically transmissiveinterface layer 307 and the second reflective surface 324 of the lightguide slab 308, or is transmitted through the optical apertures 309. Thereflections may be total internal reflections where areas 325 betweenthe light guide assembly 326 and the redirecting slab 318 are filled bya material or gas with an index of refraction that is lower than that ofthe light guide assembly. The light guide slab 308 may be made of glass,having a mirror coating 338 on its outer edge to achieve bi-directionaltransmission of light from the light source 301 through the light guideslab 308.

The light redirecting surfaces 315 a and 315 b may be shaped andarranged to collimate the light entering the redirecting slab 303through the optical apertures 309. As an example, each of theredirecting surfaces 315 a and 315 b may be a parabolic section incross-section. If the parabolic sections have focal points in or verynear the optical aperture, the light entering the light redirecting slabthrough the corresponding optical aperture will be redirected by theredirecting surfaces toward the optical output surface 120 assubstantially parallel rays, i.e., collimated light 311. This collimatedlight 311 is outputted at the output surface 320.

FIG. 3B shows an expanded section of FIG. 3A, detailing opticalapertures 309, created by the deformation of the light couplinginterface 307 which optically couple the light guide slab 308 to thelight redirecting slab 303.

With regard to FIG. 4A, an embodiment of the illumination device 400,has a light redirecting slab 418, a bi-directional light guide slab 428,a secondary optical element 402, and a light source 401. The lightredirecting slab 418 comprises a planar portion 403, having a planaroutput surface 420 and a planar face 404, and a plurality of opticalredirecting elements 405. The planar portion 403 is made of a rigid,optically transmissive material, such as glass or PMMA, and the lightredirecting elements 405 may be injection molded of soft silicone or asimilar light transmissive deformable material overmolded or bonded withan optically transmissive adhesive onto the planar face 404 to form thelight redirecting slab 418 and to serve as optical coupling elements. Inthe embodiment of FIGS. 4A and 4B, each light redirecting element 405 isprovided with an optical coupling surface 406 and two light redirectingsurfaces 415 a and 415 b.

The light guide slab 428 comprises a planar light guide layer 408 and aplurality of light steepening elements 429. The light steepeningelements 429 extend from the light guide layer 408 between thedeflecting elements 405. The light guide slab 428 guides light from thelight source 401, at least a portion of the light 412 having beenredirected by the secondary optical element 402. The light guide layer408 is made of a rigid, optically transmissive material, such as glassor PMMA. The light steepening elements 429 can be overmolded or bondedwith an optically transmissive adhesiveonto the light guide layer 408 toform the light guide slab 428. Each of the light steepening elements 429have at least one reflective surface 430 that influences the directionand steepness of the light being transmitted 412 within the light guideslab 408, and therefore moderating the output of light from the lightguide slab 428 into the light redirecting slab 418.

The steepness of the reflective surfaces 430 of the light steepeningelements 429 can increase progressively from the axis of symmetry 421 ofthe light guide slab 428 toward peripheral edge or edges 417, such thatthe angles of incidence of the light within the light guide slab 428progressively and continuously decrease from the axis of symmetry 421 tothe peripheral edge 417 to provide output light of generally balanced,uniform intensity across the light output surface 420 of theillumination device 400. Without such light steepening elements 429there would generally be a higher intensity of light 412 within thelight guide layer 408 near the light source 401, and most of the lightwould escape through the optical apertures 409 near the center of theillumination device 400. Having light steepening elements of lowersteepness near the center causes the majority of the light to beredirected away from the optical apertures 409 near the axis of symmetry421. As the intensity of light within the light guide layer 408 wouldgenerally decrease toward the peripheral edge or edges 417, the lightsteepening elements 429 progressively decrease the angles of incidenceof the light traveling within the waveguide, hence increasing theintensity of the light escaping into the light redirecting slab 418toward the peripheral edge or edges 417 and providing a more evendistribution of light intensity across the output surface 420. The outeredge or edges 417 of the light guide layer 408, may be mirror coated 438to redirect light approaching the edges back into the light guide slab428 toward the axis of symmetry 421 to be coupled into the redirectingslab 418.

FIG. 4B shows an expanded section of FIG. 4A, detailing the effect ofthe light steepening objects 429 progressively decreasing the angle ofincidence of the light 412 from the central axis of symmetry 421 to theperipheral edge or edges 417, and thereby moderating the intensity ofthe light escaping from the light guide slab 428 through the opticalapertures 409, created by the deformation of the optical couplingsurfaces 406. The function of the secondary optical element 402,redirecting light from the light source 401 into the light guide layer408, is also shown.

The light guide slab 428 may be aligned and secured against the opticalcoupling surfaces 406 of optical redirecting elements 405 by one or morefasteners such as clamps, to apply a constant and controlled pressure,thereby deforming the optical coupling surfaces 406 and creating opticalapertures 409 between the optical coupling surfaces 406 and the lightguide slab 428.

FIG. 5 shows an embodiment of an illumination device 500 including alight redirecting slab 518, a light guide slab 528, and a light source501 that lies along an axis of symmetry 521.

The light redirecting slab 518 includes a light redirecting layer 503and light transmissive interface layers 507. The light redirecting layer503 has an output surface 520 and redirecting elements 505. The lightredirecting layer 503 is made of a rigid, optically transmissivematerial, such as injection molded PMMA. Each redirecting element 505comprises two defecting surfaces 515 a and 515 b to collimate light 512from opposite directions to be outputted from and substantially normalto the output surface 520, and an optical coupling surface 506 to couplelight from the light guide slab 528. The light transmissive interfacelayers 507 may be made of soft silicone or similar material and may beovermolded or bonded with an optically transmissive adhesive onto eachoptical coupling surface 506 and thus serve as optical couplingelements.

The light guide slab 528 is composed of a light guide layer 508 andlight steepening objects 529. The light guide layer 508 is made of anoptically transmissive material, such as glass or PMMA, having a firstplanar surface 523 and a second planar surface 524. The light guidelayer 508 may optionally have a mirror coating 538 on its outer edge517. In the embodiment illustrated in FIG. 5, the light source 501 isheld within a cavity 542 of the light guide layer 508 and is opticallycoupled directly to the light guide slab 528, being. The lightsteepening elements 529, which may be overmolded or bonded with anoptically transmissive adhesive onto the first surface 523 of the lightguide layer 508, moderate the angles of light within the light guidelayer 508 and may be designed to even out the intensity of the lightoutput from a light output surface 520. Fasteners 540 may be providedfor securing the light redirecting slab 518 in a pressed positionagainst the light guide slab 528, thereby creating optical apertures 509at the surfaces 550 where the interface layers 507 are deformed by thepressure so applied, coupling each of the coupling surfaces 506 to thelight guide slab 528. As an example, the fasteners 540 may comprise (a)clamping retainer(s) applied either continuously around the peripheraledge(s) 541 of the light redirecting slab 503, or discretely at least at2 locations around the peripheral edge(s) 541.

FIG. 6 shows, in an alternate embodiment, a portion of an illuminationdevice 600 having optical redirecting elements 605 of varying size and astepped light guide slab 608 arranged to create an optical output 611 ofgenerally uniform intensity across a light output surface 620 of thedevice 600, transmitted from a light source. An optically transmissiveredirecting layer has optical redirecting elements 605 that areprogressively longer when transitioning from the center towards theperipheral edge. The redirecting layer 603 may be injection molded of anoptically transmissive material such as PMMA. The optical redirectingelements 605 have redirecting surfaces 615 and light coupling surfaces606. The light redirecting slab 618 comprises optically transmissiveinterface layers 607 made of an optically transmissive and deformablematerial such as soft silicone which extend from the optical couplingsurfaces 606 and serve as optical coupling elements. The opticallytransmissive interface layers 607 may be bonded with an opticallytransmissive adhesive or overmolded onto the optical coupling surfacelayers 606 or assembled with the optical coupling surfaces 606. When thelight redirecting slab is pressed against the light guide slab, theoptically transmissive interface layers 607 are deformed at the surface650 of the interface layers 670, creating optical apertures 609 couplinglight from the light guide slab 608, permitting light propagationthrough the optical apertures 609 of progressively larger amounts oflight from the central axis of symmetry towards the peripheral edge ofthe illumination device 600, thereby providing light of generallyuniform intensity across light output surface 620 of the lightredirecting slab 618.

FIG. 7 shows a portion of an alternate embodiment of an illuminationdevice, having a wedge-shaped light guide slab 708. An optical interfacelayer 707 which serves as an optical coupling element, can be placedbetween the light guide slab 708 and a light redirecting slab. The lightredirecting slab has defecting elements 705 including redirectingsurfaces 715 and optical coupling surfaces 706. The light guide slab 708may be secured against the redirecting slab, by a means such as but notlimited to clamping, to apply a constant and controlled pressure,thereby deforming the optical interface layer 707 to create opticalapertures 709 between the optical coupling surfaces 706 and the lightguide slab 708, and to securely hold the optical interface layer 707 inposition. In an alternate embodiment, the light guide slab may includean optically bonded or overmolded optical interface layer 707.

FIGS. 8A, 8B and 8C show a cross-section of an illumination device 800having a central axis of symmetry 821, a redirecting slab 803, abi-directional light guide slab 808, a secondary optical element 802,and a light source 801. The light redirecting slab 803 comprises aplanar portion having a planar optical output surface 820, and an arrayof light redirecting elements 805. The light redirecting elements eachhave an optical coupling surface 806 and light redirecting surfaces 815a and 815 b. The light redirecting slab 808 includes a planar portionwith a reflective surface 824 and light steepening elements 829 on theside opposing the reflective surface 824. The light steepening elements829 moderate the steepness of angles of incidence of the light 812 beingtransmitted within the light guide slab 808, thereby moderating theintensity of the light output from the light guide slab 808 into thelight redirecting slab 803.

Both the light redirecting slab 803 and the light guide slab 808 may beinjection molded of soft silicone or a similar light transmissive,deformable material. In some embodiments, the light guide slab 808 andthe secondary optic 802 may be molded as a single piece of the samematerial. The light redirecting slab 803 and the light guide slab 808are generally separated by areas 825. Light is guided by and travelswithin the light guide slab 808 via reflections on the light steepeningelements 829 and the reflective surface 824. Where the areas 825 arefilled by a material or gas with an index of refraction that is lowerthan that of the light redirecting slab 803 and the light guide slab808, light 812 undergoes total internal reflection on the lightsteepening elements 829 and on the redirecting surfaces 815 a and 815 b.The second reflecting surface of the light guide slab 808 can alsoreflect light via total internal reflection. The outer surface 817 ofthe light guide slab 808 can have a mirror or reflective coating 838 toreflect light approaching the edges back into the light guide slab 808.The light guide slab 808 may be secured against the redirecting slab803, by a means such as but not limited to clamping, to apply a constantand controlled pressure. When the light transmissive, deformablematerial of the optical coupling surfaces 806 comes into contact withfirst surface 823 of the light guide slab 808 between the lightsteepening elements 829, the redirecting elements 805 will becomeoptically coupled to the light guide slab 808, creating opticalapertures 809, to transmit light therethrough.

As in the embodiment of FIGS. 4 and 5, the light steepening elements 829moderate the angles of light within the light guide layer 508 and may bedesigned to even out the intensity of the light output from the lightoutput surface 820. The steepness of the light steepening elements 829may increase progressively from the center or axis of symmetry 821 ofthe light guide slab 828 towards its peripheral edge or edges 817, suchthat the angles of incidence of the light within the light guide slab828 progressively and continuously decreases in from the center 821 tothe peripheral edge 817, to provide output light of generally balanced,uniform intensity across the light output surface 820 of theillumination device 800. Without such light steepening elements 829there would generally be a higher intensity of light 812 within thelight guide layer 808 near the light source 801, and most of the lightwould escape through the optical apertures 809 near the center of theillumination device 800. Having light steepening elements 829 of lowersteepness near the center causes the majority of the light to beredirected away from the optical apertures 809 near the center. As theintensity of light within the light guide layer 808 would generallydecrease toward the peripheral edge or edges 817, the light steepeningelements 829 progressively decrease the angles of incidence of the lighttraveling within the waveguide, hence increasing the intensity of thelight escaping into the light redirecting slab 818 toward the peripheraledge or edges 817 and providing a more even distribution of lightintensity across the output surface 820.

The illumination device 800 may have a linear geometry or a revolvedgeometry. An illumination device 800 with a linear geometry hasredirecting elements 805 that are arranged along substantially parallellines about the axis of symmetry 821. An illumination device 800 with arevolved geometry is radially symmetric about the axis of symmetry 821,with redirecting elements 805 forming concentric rings about the axis ofsymmetry 821.

The illumination device 800 of FIGS. 8A, 8B and 8C is deformable. FIG.8A shows the illumination device 800 in its normal or resting position,where light output 811 from the output surface 820 is collimated. FIG.8B shows the illumination device 800 deformed such that the outputsurface 820 is convexly curved. In this embodiment the output light 811is non-collimated and will generally radiate away from the central axis821. In the embodiment of FIG. 8C the illumination device 800 isdeformed such that the output surface 820 is concavely curved. In thisembodiment the output light 811 is non-collimated and will generallyradiate towards the axis of symmetry 821.

FIG. 9A shows another embodiment of an illumination device 900. Theembodiment has a light redirecting slab 918, a bi-directional lightguide slab 928, a secondary optical element 902, and a light source 901.The light redirecting slab 918 includes a planar portion 903, having aplanar output surface 920 and a planar face 904, and a plurality ofoptical redirecting elements 905. The planar portion 903 is made of arigid, optically transmissive material, such as glass or PMMA, and thelight redirecting elements 905 which serve as optical coupling elementscan be injection molded of soft silicone or a similar light transmissivedeformable material overmolded or bonded with an optically transmissiveadhesive onto the planar face 904 to form the light redirecting slab918. In this embodiment, each light redirecting element 905 is providedwith an optical coupling surface 906 and two light redirecting surfaces915 a and 915 b.

The light guide slab 928 comprises a planar portion 908 having a firstplanar reflective surface 923 and a second planar reflective surface924. The light guide slab 928 guides light from the light source 901, atleast a portion of the light 912 having been redirected by the secondaryoptical element 902. The secondary optical element 902 can be locatedabove the light guide slab 928, centered about the central axis 921, andoptically coupled to the light guide slab 928 through the first planarreflective surface 923. The light guide layer 908 is made of a rigid,optically transmissive material, such as glass or PMMA.

An optical feature 938 such as a prism can be provided at the peripheraledge or edges of the light guide layer 908 to reflect the light 912 viatotal internal reflection back towards the central axis 921. Thelight-guide arrangement here provides a multipass light-guide, whichallows light to travel in the upstream and downstream directions. Lightfrom the source 901 will either enter the light-guide layer 904directly, or it will be reflected by the secondary optic 902 anddirected into the light-guide. Any light not transmitted through anaperture 909 provided at the coupling surfaces 906 of the redirectingelements 905 before it reaches the peripheral edge or edges of the lightguide layer 908 will be reflected by the optical feature 938 backthereinto. In this manner, light 912 may be reflected back and forthfrom peripheral edge to peripheral edge, until it exits the light-guidelayer 904 through an aperture 909 provided at redirectings 905,

FIG. 9B shows a revolved embodiment of he illumination device 900 havinga cross-section of FIG. 9A.

FIG. 10 shows a linear embodiment of an illumination device 1000. Inthis embodiment the illumination device 1000 has a light redirectingslab 1018, a bi-directional light guide slab 1028, and a light source1001. In this embodiment the light source 1001 is a tube shapedfluorescent bulb that runs down one edge of the light guide slab 1028.The light redirecting slab 1018 includes a planar portion 1003, having aplanar output surface 1020 and a planar face 1004, and a plurality ofoptical redirecting elements 1005 positioned parallel to one another.The planar portion 1003 is made of a rigid, optically transmissivematerial, such as glass or PMMA, and the light redirecting elements 1005which serve as optical coupling elements can be injection molded of softsilicone or a similar light transmissive deformable material overmoldedor bonded with an optically transmissive adhesive onto the planar face1004 to form the light redirecting slab 1018. In this embodiment, eachlight redirecting element 1005 is provided with an optical couplingsurface 1006 and two light redirecting surfaces 1015 a and 1015 b.

The light guide slab 1028 comprises a planar portion 1008 having a firstplanar reflective surface 1023 and a second planar reflective surface1024. The light guide slab 1028 guides light from the light source 1001for insertion into the light redirecting slab 1018. The light guidelayer 1008 is made of a rigid, optically transmissive material, such asglass or PMMA.

An optical feature 1038 such as a prism can be provided at the edgedistal to the light source to reflect the light 1012 via total internalreflection back in the direction towards the light source 1001. Anylight not transmitted through an aperture 1009 provided at the couplingsurfaces 1006 of the redirecting elements 1005 before it reaches theperipheral edge or edges of the light guide layer 1008 will be reflectedby the optical feature 1038 back thereinto.

The light emerging from the linear illumination device 1000 will besubstantially collimated in the plane. This embodiment has applicationsin computer displays and lighting. This embodiment may alternately belinearly symmetric, having a plane of symmetry with the light source1001 thereon.

There are a number of ways to achieve a broad light beam. In FIGS. 11Aand 11 B there is shown an embodiment of a semi-broad beam illuminationdevice 1100. The embodiment has a light redirecting slab 1118, abi-directional light guide slab 1128, a secondary optical element 1102,and a light source 1101. The light redirecting slab 1118 includes aplanar portion 1103, having a planar output surface 1120 and a planarface 1104, and a plurality of optical redirecting elements 1105. Theplanar portion 1103 is made of a rigid, optically transmissive material,such as glass or PMMA, and the light redirecting elements 1105 whichserve as optical coupling elements can be injection molded of softsilicone or a similar light transmissive deformable material overmoldedor bonded with an optically transmissive adhesive onto the planar face1104 to form the light redirecting slab 1118. In this embodiment, eachlight redirecting element 1105 is provided with an optical couplingsurface 1106 and two light redirecting surfaces 1115 a and 1115 b.

The light guide slab 1128 comprises a planar portion 1108 having a firstplanar reflective surface 1123 and a second planar reflective surface1124. The light guide slab 1128 guides light from the light source 1101,at least a portion of the light 1112 having been redirected by thesecondary optical element 1102. The secondary optical element 1102 canbe located above the light guide slab 1128, centered about the centralaxis 1121, and optically coupled to the light guide slab 1128 throughthe first planar reflective surface 1123. The light guide layer 1108 ismade of a rigid, optically transmissive material, such as glass or PMMA.

An optical feature 1138 such as a prism can be provided at theperipheral edge or edges of the light guide layer 1108 to reflect thelight 1112 via total internal reflection back towards the central axis1121. The light-guide arrangement here provides a mullipass light-guide,which allows light to travel in the upstream and downstream directions.Light from the source 1101 will either enter the light-guide layer 1104directly, or it will be reflected by the secondary optic 1102 anddirected into the light-guide. Any light not transmitted through anaperture 1109 provided at the coupling surfaces 1106 of the redirectingelements 1105 before it reaches the peripheral edge or edges of thelight guide layer 1108 will be reflected by the optical feature 1138back thereinto. In this manner, light 1112 may be reflected back andforth from peripheral edge to peripheral edge, until it exits thelight-guide layer 1108 through an aperture 1109 provided at the couplingsurfaces 1106 of the redirecting elements 1105.

The redirecting elements 1105 are prescribed along circular arcs 1132and 1134. The circular arcs are not concentric with the circumference1136 of the illumination device 1100. In the embodiment shown in FIGS.11A and 11B, the centers of the circles that prescribe the arcs 1132 and1134 are equidistant from the center 1121 of the illumination device1100 itself. The resultant beam from the output surface 1120 will becollimated in the YZ plane and divergent in the XZ plane.

FIGS. 12A and 12B show a revolved illumination device 1200 includinglinear and parallel cylindrical lenses 1210, for collimating light, onthe output face 1220. The illumination device also includes a lightsource 1201, and optionally, a secondary optical element 1202 (asupplementary light dispersal optic feature) directing the transmissionof light from the light source 1201 into a light guide slab 1208,further comprising an optically transmissive interface layer 1207 thatis an optical coupling element between the light guide slab 1208 and alight redirecting slab 1203. The light redirecting slab 1203 includes agenerally planar portion 1204 having an output surface 1220 and aplurality of revolved optical redirecting elements 1205, the opticalredirecting elements 1205 each have an optical coupling surface 1206situated distally from the output surface 1220.

The light redirecting slab may be made of any suitable opticallytransmissive material, such as glass or injection molded poly(methylmethacrylate) (PMMA). The light guide slab 1208 may similarly be made ofany suitable optically transmissive material, such as glass or PMMA, andhas an input surface 1222 for accepting light from the light source1201, a generally planar first surface 1223 and a generally planarsecond reflective surface 1224. The optically transmissive interfacelayer 1207 may be comprised of a soft material such as silicone which isdeformable under an applied pressure, and is overmolded, or chemicallybonded with an optically transmissive adhesive to the planar firstsurface 1223 of the light guide slab 1208. The light guide slab 1208 andthe optically transmissive interface layer 1207 are collectivelyreferred to as a light guide assembly.

The light guide slab 1208 is optically coupled to and receivestransmitted light directed from the secondary optical element 1202through the input surface 1222. Optical bonds creating optical apertures1209 for coupling light from the light guide slab 1208 to the lightcoupling surfaces 1206 of the light redirecting slab 1203 are formed ateach optical coupling surface 1206 of the optical redirecting elements1205 when the light redirecting slab 1203 is pressed onto the opticallytransmissive interface layer 1207. The light guide slab 1208 isotherwise separated from the light redirecting slab 1203 by areas 1225which can be air gaps.

The resultant illumination device 1200 produces a broad beam, which isdivergent in the YZ plane and collimated in the XZ plane.

FIGS. 13A and 13B show an illumination device 1300 with a light source1301 positioned at one edge of the illumination device 1300. Theillumination device also includes a light guide slab 1308, furthercomprising an optically transmissive interface layer 1307 that is anoptical coupling element between the light guide slab 1308 and a lightredirecting slab 1303. The light redirecting slab 1303 includes agenerally planar portion 1304 having an output surface 1320 and aplurality of optical redirecting elements 1305 being, in cross section,concentric portions of circles of increasing diameter with their centerpoint 1321 in the vicinity of the light source 1301, the opticalredirecting elements 1305 each have an optical coupling surface 1306situated distally from the output surface 1320. The light redirectingslab 1303 further includes linear and parallel cylindrical lenses 1310on the output face 1320. The light source 1301, in this embodiment canbe an LED, a compact fluorescent tube, a small incandescent light bulbor solar light transmitted via optical fibres.

The light redirecting slab 1303 in the present embodiment can be made ofany suitable optically transmissive material, such as glass or injectionmolded PMMA. The light guide slab 1308 is wedge shaped, in crosssection, and can similarly be made of any suitable opticallytransmissive material, such as glass or PMMA. The light guide slab 1308has an input surface 1322 for accepting light from the light source1301, a generally planar first surface 1323 and a generally planarsecond reflective surface 1324. The optically transmissive interfacelayer 1307 may be comprised of a soft material such as silicone which isdeformable under an applied pressure, and is overmolded, or chemicallybonded with an optically transmissive adhesive to the planar firstsurface 1323 of the light guide slab 1308. The light guide slab 1308 andthe optically transmissive interface layer 1307 are collectivelyreferred to as a light guide assembly.

The light guide slab 1308 is optically coupled to and receives lightfrom the light source 1301 through the input surface 1322. Optical bondscreating optical apertures 1309 for coupling light from the light guideslab 1308 to the light coupling surfaces 1306 of the light redirectingslab 1303 are formed at each optical coupling surface 1306 of theoptical redirecting elements 1305 when the light redirecting slab 1303is pressed onto the optically transmissive interface layer 1307. Thelight guide slab 1308 is otherwise separated from the light redirectingslab 1303 by areas 1325 which can be air gaps. The overall shape of theillumination device 1300 need not be circular but can be square,triangular, or any appropriate shape. The resultant illumination device1300 produces a broad beam, which is divergent in the YZ plane andcollimated in the XZ plane.

Varying modifications and improvements of the above describedembodiments, and to the optical coupling interface disclosed in thecontext of the device and method herein will be apparent to thoseskilled in the art, without departing from the scope of the invention asdefined by the appended claims.

What is claimed is:
 1. An illumination device comprising: at least onelight source; a light redirecting slab made of optically transmissivematerial and comprising an optical output surface and an array ofoptical redirecting elements, each of the optical redirecting elementshaving an optical coupling surface situated distally from the opticaloutput surface and at least one light redirecting surface for receivinglight from the optical coupling surface and redirecting the lightreceived therefrom toward the optical output surface for emissiontherefrom; a substantially planar light guide slab made of an opticallytransmissive material and having a first surface, a second surfaceopposite the first surface and at least one input surface, the at leastone input surface for receiving light from the at least one lightsource; at least one optical coupling element made of a deformable,light-transmissive material; and an array of optical apertures opticallyinterconnecting the light guide slab and the light redirecting slab, theoptical apertures formed by interfaces between at least one of the firstsurface of the light guide slab and the optical coupling surfaces of thelight redirecting slab, and the at least one optical coupling elementdeformed by pressure at the interfaces; wherein the first surface, thesecond surface and the at least one deformed optical coupling elementare arranged one with respect to the other such that light entering thelight guide slab is guided through the light guide slab via one or morereflections for insertion into the light redirecting slab.
 2. Theillumination device of claim 1, further comprising at least onesecondary optical element for redirecting at least a portion of thelight from one or more of the at least one light source into the lightguide slab, each secondary optical element in optical communication withone or more of the at least one input surface of the light guide slaband with one or more of the at least one light source.
 3. Theillumination device of claim 2, further comprising at least onedeformable secondary optical coupling element, each secondary opticalcoupling element coupling one of the at least one optical input surfaceof the light guide slab to an optical exit surface of one of the atleast one secondary optical element.
 4. The illumination device of claim2, wherein one of the at least one secondary optical element is situatedabove the light guide slab and one of the at least one light source. 5.The illumination device of claim 1, wherein the at least one deformedoptical coupling element is a single optically transmissive interfacelayer disposed between the light guide slab and the light redirectingslab to form the array of optical apertures.
 6. The illumination deviceof claim 1, wherein the at least one deformed optical coupling elementis a plurality of optically transmissive interface layers, each one ofthe plurality of optically transmissive interface layers disposedbetween the light guide slab and the optical coupling surface of one ofthe array of optical redirecting elements to form one of the array ofoptical apertures.
 7. The illumination device of claim 1, wherein the atleast one deformed optical coupling element is at least a portion ofeach of the optical redirecting elements including the optical couplingsurface of the optical redirecting elements.
 8. The illumination deviceof claim 1, wherein the deformed optical coupling element comprises asoft polymer material that is elastomeric.
 9. The illumination device ofclaim 1, wherein the optical output surface comprises collimatingelements.
 10. The illumination device of claim 1, wherein the opticaloutput surface is substantially planar.
 11. The illumination device ofclaim 1, wherein the at least one light redirecting surface redirectslight via total internal reflection.
 12. The illumination device ofclaim 1, wherein each of the at least one light redirecting surfaceincludes a parabolic section in cross-section.
 13. The illuminationdevice of claim 1, wherein each of the optical redirecting elementscomprises a first light redirecting surface for receiving light thatgenerally travelled in a first direction through the light guide slaband a second light redirecting surface for receiving light thatgenerally travelled in a second direction, opposite the first direction,through the light guide slab, both of the first and the second lightredirecting surfaces being optically coupled to the optical couplingsurface of the said optical redirecting element and being arranged toredirect light impinging thereon toward the optical output surface; andwherein at least one peripheral edge of the light guide slab comprises areflective element to reflect light that would otherwise escape from thelight guide slab back into the light guide slab.
 14. The illuminationdevice of claim 13, wherein the reflective element is a mirror coating.15. The illumination device of claim 13, wherein the reflective elementis a prism for redirecting light via total internal reflection back intothe light guide slab.
 16. The illumination device of claim 1, whereinthe first surface and the second surface of the light guide slab aresubstantially planar and parallel to one another.
 17. The illuminationdevice of claim 1, wherein the light guide slab is generallywedge-shaped and tapers away from the at least one light source.
 18. Theillumination device of claim 17, wherein the first surface of lightguide slab is stepped.
 19. The illumination device of claim 1, whereinthe first surface of the light guide slab comprises a planar light guidelayer and a plurality of light steepening elements extending from theplanar light guide layer, each of the light steepening elementscomprising at least one reflective surface for moderating the steepnessof angles of the light being transmitted through the light guide slab toprovide output light of generally uniform intensity across the lightoutput surface, the steepness of the reflective surface increasingprogressively from the at least one light source toward a peripheraledge of the light guide slab.
 20. The illumination device of claim 1having a linear geometry, wherein the optical redirecting elements arearranged in parallel lines.
 21. The illumination device of claim 20,wherein the at least one light source is located along a peripheral edgeparallel to the optical redirecting elements.
 22. The illuminationdevice of claim 1 having a central axis, wherein the at least one lightsource is located along the central axis and wherein each of the opticalredirecting elements are annular, of a sequentially increasing diameterand concentrically arranged about the central axis.
 23. The illuminationdevice of claim 1, wherein: the optical redirecting elements are annularand are located along substantially concentric circle arcs; and theinput surface is shaped as a circle arc substantially concentric withthe optical redirecting elements and forms a portion of the peripheraledge of the light guide slab.
 24. The illumination device of claim 23,wherein the light redirecting slab has a circular circumference, and theconcentric circle arcs along which the optical redirecting elements arelocated are eccentric with the circular circumference of the lightredirecting slab.
 25. The illumination device of claim 1, wherein theoptically transmissive material of both the light redirecting slab andthe light guide slab is elastomeric.